1. Field of the Invention
This invention relates to a frequency selective optical coupler which is particularly useful in fiber optic waveguide multiplex communication systems.
2. Description of the Prior Art
Fiber optic communication systems have been developed to the point where they appear to be able to provide reliable long distance communication channels. While use of such systems considerably reduces the cable size and weight for a given bandwidth, generally only a single light beam is transmitted via each specific fiber, since there has been no satisfactory structure for segregating the various wavelengths of light which might carry different signals on a single fiber. One known device, described in U.S. Pat. No. 3,905,676 issued Sept. 16, 1975, employs uniform periodic diffraction gratings to provide selective coupling of a particular wavelength band of light exiting a fiber.